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Surface Water Management

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Surface Water Management

Within our 10 year Business Plan (2016 – 2025) we aim to deliver effective drainage and protect the island’s environment by reducing the risk of sewer flooding and pollution.

Flood and Pollution Risk

Our sewer network takes the island’s wastewater to our treatment centre at Belle Greve and in many places, also collects rainwater from roof and road drainage.  Here rain runs off vast areas of impermeable surfaces straight into the sewer network which struggles to cope with the increased volumes. The capacity of these sewers can however become overloaded during heavy rainfall.   To prevent flooding diluted flows can be directed into our coastal waters through our combined sewer overflows (CSOs).  However, in more extreme cases this can cause serious flooding where the sewers back up damaging properties as well as the island’s infrastructure.

Future Challenges

Rainfall runoff is becoming harder and harder to manage in built up urban areas.   New developments, often built on greenfield land, and urban creep (extensions to existing properties and paving of driveways) all add to the speed of runoff water into our sewers.  The exacerbation of this by climate change threatens to continue in the future. 

Once storm water enters the network it becomes a burden for us to pump, treat and dispose of.  By contrast, in its natural state this rainwater would have normally soaked away in to the soil, streams, reservoirs or even out to sea without any requirement for human intervention.

A Sustainable Approach

The removal, or slowing down of surface water from the sewage system, reduces flood and pollution risk as well as creating headroom for predicted further development on the island. Traditional storage tank solutions are expensive, often limited by space, can leave long term legacies of operation and maintenance and require upsizing as volumes increase. The most effective way of adapting to this over the long-term will be through managing storm water using sustainable drainage systems referred to as SuDS.

SuDS aim to mimic natural water management practices and are designed to drain surface water in a way that will provide a more sustainable approach than the conventional practice of routing run-off through a pipe to a watercourse, in order to reduce risk of flooding.   Guernsey Water is actively promoting the use of sustainable drainage on all developments on the island and in particular retrofit scenarios with existing infrastructure.


 For a full copy of the Surface Water Management Policy, click here

Local case studies

Vauvert Primary School

Read the case study of our first sutainable urban drainage project at Vauvert Primary School here.



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